The article has been automatically translated into English by Google Translate from Russian and has not been edited.

Will the mask protect against COVID-19 in the pouring rain, frost and in the sauna: the answer of scientists

'15.10.2020'

Source: Inosmi.ru

Autumn rains made the world think about the effectiveness of using masks in different weather conditions. Finnish experts told how different types of masks are arranged, and which of them are more effective in what conditions, writes Inosmi.ru.

Photo: Shutterstock

WHO and the UK's National Health Service have warned of a possible decrease in the effectiveness of the protective function of masks in the rain and at high levels of humidity. Now this topic is especially actively discussed where the autumn rainy season began.

Tim Spector, Professor of Epidemiology at King's College London, said it was necessary to change masks in wet and wet weather more often than usual.

“One should also take into account the humidity arising from human breathing. I think the microclimate that forms when wearing a mask will be of decisive importance in most cases. Probably, this problem has become especially urgent there now. It is important to remember that masks are needed primarily in rooms that do not provide space for keeping distance or are not ventilated, ”says Hannu Salmela, head of the VTT research group.

Health officials have already started talking about the peculiarities of using masks in the fall, for example, the need to change masks more often on rainy days. Salmela believes in common sense when the weather changes.

“If the mask gets rain and gets wet, its protective properties may change. It is also bad if the filter gets wet through, ”the expert warns.

In such a situation, many will change the mask to a dry one, simply for convenience reasons, and healthcare representatives may well do without additional reminders to the population.

Which type of mask is more effective in humid climates

The effectiveness of a three-layer mask is usually provided by an inner nonwoven layer that generates static electricity. This layer effectively blocks particles from 0,65 to 7 micrometers. Over time, the charge level decreases, and with it the protective properties of the mask.

“Typically, surgical masks are tested for four hours in an 85 percent humidity environment. In everyday situations, masks are recommended to be changed approximately once an hour. I do not see the need to adjust this recommendation due to the changing weather, ”says Salmela.

In addition to the industrially tested masks, many use their own masks.

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Their effectiveness in rain and other conditions is unknown. They are usually less effective than regular masks, but they can stop splashes when sneezing and coughing.

While approved surgical masks block the spread of 95-98% of the particles that cause the coronavirus, homemade cotton masks have shown a 10-20% result in testing. Based on the test results, snood fleece scarves only increase the number of drops: the fabric breaks large drops into many small ones.

Hannu Salmela recalls that the standard so-called three-layer masks are designed to withstand the moisture generated by breathing. In addition, the top layer of the mask is water-repellent and may be coated with a substance that prevents the tissue from absorbing liquids. The inner layer also repels moisture.

The nonwoven fabric for the outer and inner layers of the mask is often made from polypropylene. This is the same non-water-absorbing plastic used to make clotheslines or cables that are covered in ice for months.

The degree to which homemade masks get wet may depend, for example, on what material they are made of. Natural materials, including cotton, have the strongest absorption properties.

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Certified masks are generally tested on the assumption that they will be exposed to moisture when used under real conditions. It is caused by the water vapor produced on exhalation.

“Typically, surgical masks are tested at 85% relative humidity and approximately 21 degrees Celsius,” says Salmela.

85% RH is fairly humid weather, but not a rainy day. This indicator roughly coincides with the level of moisture in human respiration.

With decreasing air temperature, the level of humidity also decreases. In autumn and winter, humidity is lower than at 21 degrees Celsius. What should we do when the temperature is below zero degrees?

Will the mask save you in the cold?

Basically, the mask should work.

“In severe frosts, the exhaled air will settle and freeze on the mask, and then its effectiveness will decrease. Surgical masks are not tested in cold conditions. Before the start of the tests, the masks are placed in a temperature regime of minus 30 degrees for 24 hours and in conditions of plus 70 degrees for the same period of time, ”says the expert.

Winter frosts are changing the dynamics of the spread of coronavirus by droplets. In dry, frosty air, droplets and the particles of coronavirus contained in them become more easily small aerosols that can penetrate deeper into the respiratory system. In winter, indoor air humidity also decreases, which can also affect the spread of the virus.

Does the mask at outdoor events protect if someone screams?

“On the street, you also need to keep a distance, and if this is not possible, you must wear a mask. It is important to understand that we use masks primarily to protect those around us - especially if we are going to actively “get sick”, ”says Salmela.

At hockey matches, masks are especially important, because hockey matches are held in indoor stadiums.

The European standards makers approached the laboratory test requirements very wisely. To study the resistance of the mask and simulate breathing, a tube with a diameter of 25 millimeters is used - which roughly coincides with the opening formed by the lips of a screaming fan.

Do you need a mask in the sauna?

Sauna is a typical room where it is difficult to keep distance between people. The effectiveness of masks is usually checked after placing them in a temperature regime of plus 70 degrees - in Sweden this is quite suitable for the description of a heated sauna.

“I see no need and do not recommend using masks in the sauna. There the relative humidity and temperature can rise very high and masks are not suitable for such conditions, ”sums up Hannu Salmela.

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